This disclosure relates to a machine including a compact, high power density gear case for transmitting rotational power from a drive to a driven member, and, more particularly, to such a gear case including an improved cooling system.
A variety of different apparatuses exist for mining coal and other materials from underground seams. One apparatus that is commonly used in underground mining operations comprises a continuous mining machine used in instances where extended portions or longwalls of seam are desired to be mined. Such longwalls may, depending upon the seam configuration, extend for distances of 300-1200 feet. It is standard practice in this type of mining to mine parallel entries into the seam to be mined and connect those entries with one or more primary passages. Such arrangement defines the longwall pillar(s) to be mined. The roof of the primary passages is usually supported by movable roof supports during the mining of the exposed “face” of the longwall pillar.
Conventional longwall mining techniques employ a mining machine that is known in the industry as a longwall shearer. A longwall shearer typically has an elongated mobile frame that is supported on floor-mounted tracks that are adjacent and substantially parallel to the mine face. Rotary driven toothed drums are operably supported on arms on each end of the elongated frame for winning the coal as the frame passes back and forth before the mine face. The won material falls into a face conveyor that is usually attached to the floor-mounted tracks and extends parallel to the longwall face. The face conveyor discharges the material onto other conveying apparatuses to transport the material from the seam. As the mine face recedes, the conveyor and track assembly is advanced forward to enable the shearer to continue mining.
As shown in FIG. 1, a longwall shearer mining machine 10 has an elongated mobile frame 12 that is movably supported on a conveyor/track way 14 that is substantially parallel with the longwall face 15. A laterally extending rotary drum 18 which has a plurality of mining bits 19 attached thereto is pivotally attached to each end of the elongated mobile frame 12 by a corresponding ranging arm 16. The operation of the shearer 10 is well known in the mining art and, as such, will not be discussed in detail herein. However, the skilled artisan will appreciate that the shearer 10 is moved back and forth on the track way 14 such that the mining bits 19 on the rotating drums 18 can be brought into engagement with the mine face 15 to dislodge material there from. As the face recedes, the track way 14 and shearer 10 are advanced towards the face 15 to enable the mining process to be continued.
Gear cases used in the ranging arms of longwall shearers are required to be very power dense. This is because the theoretical output of a mining machine is proportional to its installed power, while the operating envelope in a mine requires the package to be as small as possible. The heat generated in these powerful gear cases must be removed on a continuous basis to promote long-term reliability.
Longwall shearer ranging arm gear cases are specialized in nature. They are required to be as compact as possible while being capable of reliably transmitting rotational power to the shearer cutting drum. As with many gear cases with high power density, heat is generated from the losses in the rolling elements and the windage energy of the lubricant. In order to prevent the gear case from overheating and damaging the lubricant, seals and other components, it is common to incorporate some method of cooling the unit.
Further, ranging arm gear cases are required to have a specific shape to make them long enough to extend between the input motor and the output shaft. Owing to this characteristic, they usually have a number of single gears, known as reach gears, mounted in a row (usually 2 to 5) to space the input and output shafts apart. A substantial portion of the heat in the gear case is produced as each of these gears churns at high speeds in the lubrication oil around the gears. Additionally, the friction of their rolling element bearing further contributes to the heat making.
Conventional ranging arm gear case designs utilize either a separate water-cooled heat exchanger that is mounted in the oil reservoir, or a heat exchanger built into the housing of the gear case.
Both of these methods require the gear case to be moderately larger in size and of increased cost of manufacture. In both cases there is also a risk of contamination of the internal lubricating oil with water from a leak in the heat exchanger or water and dirt ingress from the environment due to the required openings in the housing to bring the water into and out of the unit.